This invention is directed to a valve which controls the vacuum applied to the left ventricle during open-heart operation, prevents reverse flow to the heart, and vents the line of gas or blood should pressure rise above atmosphere.
During some open-heart procedures, even though the heart is bypassed with the open-heart tubing, some blood finds its way into the left ventricle of the heart. Unless the blood is drained from the left ventricle, the blood causes the heart to distend. Such distension makes it difficult or impossible to resuscitate the heart at the end of the procedure. For this reason, some surgeons attach a slender tubing to the left ventricle to drain the blood from it. A suction pump may be used to provide the vacuum to remove the blood. Several problems may be caused by such a method. One problem arises if the opening of the drain line tube attaches itself to the inside of the heart chamber. This causes suction to be stopped, and the tubing must be wrenched away from the tissue. This causes trauma to the chamber tissue. The valve enables the surgeon to regulate the suction intensity to the desired level so that it is easier to pull the tube away from tissue. It has been found in clinical trials that 150 mm Hg is a good compromise between suction and adhesion to tissue.
Another problem which may occur during left heart venting arises from the fact that the amount of suction to the heart through the left ventricle drain line is regulated by the speed of the vacuum pump. The vacuum pump is controlled by the heart-lung machine technician so that the surgeon must communicate to the technician the amount of suction desired. Many times, suction intensity is either too great or too little.
Another problem which may occur in such an organization is the buildup of pressure in the left ventricle drain line. This would drive air into the heart and cause an air embolism and even possible death of the patient. Such inadvertent pressure in the left ventricle drain line could be caused by any one of several means. For example, the vacuum pump switch could accidentally be positioned to run the pump in reverse so that instead of suction, pressure would be produced in the drain line. Another possible cause of such pressure would occur when the suction pump is connected to discharge into a closed reservoir in which the pump causes a pressure buildup. In such a case, there is a chance that when the pump is stopped, the pressure may leak back through the drain line into the heart. Another cause of pressure buildup in the drain line is in the structure of the roller pump. In a roller pump, the tubing may be accidentally inserted in a backward orientation into the pump housing so that even if the pump switch is in the "Forward" position, the pump is working backward.
In order to prevent such problems from causing dangers to the patient, the present left ventricle vacuum control and pressure relief valve was created. This valve enables the surgeon to personally set the suction level at the operating table instead of at the pump, which he cannot conveniently reach. In this case, the pump can be left running at one speed, and the surgeon can adjust the suction pressure at his convenience. In addition, this valve prevents flow toward the heart and allows flow only away from the heart, whether the flow be blood or air. Furthermore, the valve of this invention permits any pressure in the downstream line to be vented to the atmosphere instead of being transmitted to the heart. When the venting is accompanied by the escape of blood from the valve, the surgeon is immediately notified that something is wrong (for example, there is inadequate suction to remove the blood) and can take corrective measures.